In island grid applications, generating assets, such as diesel or gas powered generators and turbines, may experience transient load conditions that can cause changes in grid frequency and voltage. These transient conditions may include, for example, large load changes and sudden changes in power source availability, such as a fuel-powered generator shutting down or a variation in supply from a generating asset such as a wind or solar generator. Such variations in line frequency may result in dropped loads or damaged equipment. Such problems may be particularly pronounced in systems that use engine/generator sets powered by natural gas or other lower energy density fuels.
Island grid generators are often sized with significant excess rated continuous power capacity in order to carry peak loads, respond to large transient load steps, and provide redundancy in support of mission-critical operations. They may operate at very high utilization rates, for example, 24 hours a day, 7 days a week, 365 days a year, but at relatively low real load factors, commonly between 15-50%, for extended periods of off-peak time. Furthermore, manufacturer warranty requirements may result in additional costs due to the use of self-imposed, manual load banks. This operating profile may result in lower fuel efficiency, excessive wear and tear on generators, and notable increases in particulate matter (PM) and hydrocarbon (HC) emissions due to the incomplete combustion of diesel or natural gas fuel.
In island grind and other off-grid applications, the magnitude of load steps can exceed the incremental step capability of the available generation. In these cases, the load steps can cause under/over voltage or frequency of the load bus. This may result in damage to any grid-connected devices, such as motors and transformers and the like, that are typically designed to operate at or near the nominal voltage and frequency. Because of the potential for such damage, a generator may have protective circuits that disconnect the generator from the load bus, thus protecting such equipment but resulting in a possible blackout or loss of load. In some demanding applications, there are loads that require huge current magnitudes which would require multiple parallel generators to meet this demand to start these demanding loads and maintain the power and reactive components within the generator specifications under transient conditions. Once the load is started, the steady state load is relatively small, which does not require the operation of all these generators. The load steps can be predominately resistive which results in a change in active power. Load steps can also be reactive, which results in a change in volt-Amperes Reactive (VAR).